The present invention relates to a new and improved construction of an actuation device or mechanism for a drive element, such as a drive gear of a weft thread carrier of a shuttleless loom, the weft thread carrier being guided by a gripper tape or band or the like.
Generally speaking, the actuation device of the present development is of the type wherein the drive gear is operatively connected with a crank drive by means of a transmission element of a slipless traction means-power transmission or drive. This crank drive moves to-and-fro a linearly guided carriage or slide which is connected for movement with the traction means-drive.
Equipment of this type is required, for instance, at so-called rapier or gripper looms, in order to impart the requisite to-and-fro movement to the gripper bands or tapes for the alternate weft thread insertion into the shed and for weft thread transfer from one gripper to the other. The drive mechanism in conjunction with the gripper tapes are located upon the sley which oscillates back-and-forth.
An actuation device suitable for this purpose is known to the art from German Patent No. 2,637,819, granted July 19, 1979 wherein the crank drive actuates a pivotal or oscillatory lever which is mounted coaxially with the drive gear and there is provided a drive belt pulley or disc fixedly connected with the drive gear. The pivotal or oscillatory lever carries at its free end a respective deflection roll or roller for each run or strand of a toothed belt which is trained about the belt pulley or disc. The ends of the belt strand or run are each retained in fixed anchors at the loom frame.
From the publication "Melliand Textilbericht" 6/1977, pages 469 et seq. and from the German Patent publication No. 2,628,402, published Dec. 30, 1976, there are known in this technology actuation devices of the aforementioned type wherein a linearly guided slide shoe provided with a respective deflection roll for each run of a toothed belt which trains about the drive pulley or disc of a drive gear is actuated by a crank drive. Each belt run is guided between the slide shoe and the drive belt pulley means of a respective deflection roll arranged in the extension of the path of movement of the slide shoe and the belt run ends likewise are each fixedly anchored at the loom frame.
There heretofore known actuation devices possess the common drawback that the laws of motion of the weft thread-insertion means is uncontrollable, since the belt strand or run which is tensionally loaded in each instance possesses an appreciable length and therefore is capable of extensively elongating. In particular, the dead-center points of the weft thread-insertion means can alter as a function of the rotational speed of the loom, since the traction forces, and thus, the belt elongation can vary, as is known, as a function of the square of the rotational speed. Consequently, there exist appreciable difficulties at looms equipped with a respective weft insertion element penetrating from each side into the shed wherein the weft thread is transferred from one insertion element to the other, since the inter-engagement of the gripper heads is decisive for proper thread transfer, both as concerns the mutual penetration depth of the insertion elements and also with respect to the relative velocity thereof. Additionally, an accommodation of the weft thread-insertion drive to different cloth or fabric widths only can be accomplished by performing cumbersome and time-consuming resetting operations at the belt drive and at the anchoring points of the belt ends, if it is intended to maintain the precise dead-center position of the weft insertion means in the shed because of the weft thread transfer as well as the belt tension.
Moreover, this belt tension changes during the course of the oscillatory movement of the pivotal or oscillatory lever carrying the deflection roll of the equipment disclosed in the aforementioned German Patent No. 2,638,819, because the circular configured path of movement of the deflection rolls deviates markedly from an ellipse, with the anchoring points constituting the focal points, which such deflection rolls must describe, in order that the total length of the belt sections remains constant between the deflection rolls and the anchoring points.